Mike in CA

Thanks Pete, for the informative (as always) post.

TRAKCAR

+1 thanks Pete..

hzoenvy33

One last point:

A friend of mine is working for a um "known" French tire manufacturer.. he said, the 918 tire is just awesome. Not just a good tire, another semi-slick, what ever. It is really awesome.

Therefore, Porsche is going to use it on the .3 RS.

I don't have any experience in tires (I'm a aero and thermal guy), so I'm not sure if they could "just" build a 20inch tire with the same performance, therefore I can just quote him: "They would be stupid not to use it".

TrackFan

Unsprung revolving weight is something to be kept as light as possible for best performance. Also, the sidewalls of a 21" tire is getting damn small. This might work on smooth tracks, but rough bumpy tracks will make the tire want to skip across the surface. This will be really noticeable on the street. Not to mention a rough ride.

They'll have to soften the suspension to help this problem. I'd prefer to have firmer suspension, and more give in the tires.

Personally, I think they look goofy too. Reminds me of low riders.

This is a proper look.

Petevb

The sidewalls are no shorter than on the 991 GT3, or indeed the 997 GT3 or RS; they are actually taller. That plus the larger rolling radius may in fact help the ride quality.

As for weight, if that was the only concern performance cars would all come with go-kart wheels. It's all a trade-off, in this case for increased grip.

TrackFan

The sidewall would have to be shorter unless they increased the outside diameter. Is that what they did?

Even with a bit more grip. They lose acceleration, and braking with the extra weight. I'd be curious to see lap times for a 21" tire compared to going the other way, and using an 18" tire.

Billy Wyatt

For some reason i believe Porsche knows what they are doing....

TrackFan

Yes, they know how to make money.

How many do you think would accept a smaller wheel on the RS?

Petevb

As has been mentioned many times over the last 3 pages, ie see here, yes that's what they did.
28.7" OD for the RS vs 27.2" for the GT3.

Acceleration when they are not traction limited will be less, when traction limited (ie coming off the corners) will be more. Braking will be up due to the increased grip.

The interesting discussion is feel- a narrow slip angle tends to be harder to drive, and often IMHO less fun. In terms of numbers, however, it's going to be fast.

TrackFan

It just seems like it's going in the wrong direction. The goal for any race car is to keep the tire/wheel combo as light as possible. The little grip gained is lost on the extra rotating weight that has to be stopped. Which take more brake pressure.

I wasn't aware the GT3 had a traction problem with it's present HP?


btw I'm in no way arguing with you. This is my favorite subject, and I enjoy talking about it.

Petevb

Not true, or as I said we'd all be running go-kart wheels. You do want low weight, but you need to balance this with size for grip.
Any car's lap time is primarily limited by grip. For time (as opposed to fun) there is no such thing as "too much".

TrackFan

I guess we'll just have to agree to disagree.

I'm not convinced adding weight to a wheel/tire is the best way to more performance.

Some think it looks cool though.

Mike in CA

So you would be ordering PCCB's then, to save 8-10 pounds of un-sprung weight per corner to be as light as possible for the best performance, which is much more than the weight difference even between 18" and 20" wheels? No? Too expensive to purchase and replace, perhaps?

Fair enough, but it just points out how there are few perfect answers and almost always trade offs in any given engineering solution. Apparently Porsche feels that the minor increase in weight of a 21" wheel over a 20" wheel is more than offset by the need for more grip at the rear of the RS. I suspect the chassis designers wouldn't go to a staggered wheel setup unless they saw a net benefit to doing so.

TrackFan

If I was so serious about lap times that money didn't matter. Yes, i'd use PCCB brakes. Lighter is better.

It's not just the weight of the wheel. The tire is heavier too. You also have the cost of those 21" tires if cost is a problem.

CAlexio

I have to disagree.. I believe branding and product differentiation are much greater values to Porsche and other manufacturers than what we naively believe. If Porsche decided that they wanted to differentiate the Rs more than in the previous generation, so that they can charge significantly more do the RS vs the gt3, then they need to find enough visual features to include to make this price delta worthy in a customer's eyes. mechanical matters also, but visual differentiation comes first because these are passion and impulse purchases. A "real" racer buys a stripped out fast car, the RS, let's be frank.. Treads that fine line between poseur and ultimate roadable track car.

If you agree with my statement above, then I would conclude that the 21" wheels and other features are added as long as they do NOT plausibly reduce performance, as long as the visual and brand differentiation outweighs the potential decrease in usability (21" R compound tires for example).

I realize this may not be a popular view, but I really think that as consumers we need to be a bit more critical and open eyed... We all know why there isn't a 3.8L cayman yet right?... All together now... MARKET SEGMENTATION!!!!!

So about that rear wing on the RS, I heard only the limited edition versions will be allowed in red.. Because red was tested to be a whole second faster around the 'ring ;-)